<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <button>事件监听</button>
    <script>
      var btn = document.querySelector('button')
      btn.addEventListener('click', function () {
        alert('事件监听')
      })
      btn.addEventListener('click', function () {
        alert('又是事件监听')
      })
    </script>
  </body>
</html>
